WEBVTT
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In this step, we're going to
recap some of the logic gates
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we have already made and
look at all the other gates.
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You should be familiar, by
now, with the basic NAND
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gate and its truth table.
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In the last step, we also tied
the two inputs of a NAND gate
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together.
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In this configuration, when
the switch was turned on,
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the lamp turned
off, and vice versa.
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This set up is
also known as a NOT
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gate, which has this symbol.
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In the video, we also went over
the construction of an AND gate
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and showed you that truth table.
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You also independently put
some NAND gates together
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and worked out the
truth table, that
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should have come out like this.
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This is actually
called an OR gate.
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Another type of gate we can
make is called an XOR gate.
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It can be assembled from
four NAND gates, like this.
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This is the symbol
for an XOR gate,
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and here is its truth table.
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Any of the basic gates can
be combined with a NOT gate
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to reverse the output.
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An "N" is then placed
with the name of the gate,
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and a small circle added to
the output end of the symbol.
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So when an AND gate is
combined with a NOT gate,
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it produces a NAND gate, which
you're already familiar with.
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An OR gate and a NOT
gate produces a NOR gate,
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and an XOR gate with a NOT
gate produces an XNOR gate.
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So here's a summary
of all the logic
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gates with their
NAND equivalents,
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and also their truth tables.
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There is a downloadable
PDF of this summary
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at the bottom of this step.
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In the next step, there's going
to be a quiz on truth tables
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and logic gates, so
it might be worth
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spending a little time reviewing
the previous steps in this week
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to ensure that you can answer
all the quiz questions.
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